The present invention relates to a vehicle seats, and in particular to hydraulically or fluid powered adjustable automotive vehicle seats.
Adjustable vehicle seats are provided to comfortably accommodate various sizes and shapes of vehicle occupants. Typically at least the fore and aft position of the seat along with the angle of the seat back are adjustable via suitable adjustment and locking mechanisms. Other adjustment of the seat position, and/or parts of the seat, for example adjustment of the seat height and/or tilt, or of the headrest or lumber support position, may also be provided. The seat adjustment mechanisms may be manually operable, or increasingly some or all may be power operated. Conventionally such power operated adjustment mechanisms comprise separate individual electric motors mounted within the seat driving each adjustment mechanism though suitable gearing.
Hydraulic or fluid powered seat adjustment mechanisms in which pressurised fluid provided from a pump, is supplied via a control valve to piston/cylinder actuators to adjust the position of the seat or portions of the seat, have been proposed instead of electric powered systems. Indeed the earliest of such proposals date back a number of years. An example of such a powered hydraulic adjustment systems is described in U.S. Pat. No. 5,435,625. A simple telescopic powered hydraulic seat height adjustment arrangement is briefly described in GB 2,167,494.
Hydraulic or fluid powered arrangements offer the prospect of extremely quiet, near silent, operation, without the noisy mechanical gearing. Smooth and almost infinitely variable adjustment is also possible with such hydraulic powered arrangements.
In spite of these, and other, advantages of hydraulically powered seat adjustments have not been adopted for widespread automotive vehicle seat use over the considerable number of years since they have initially been proposed. Overall, and although hydraulics are used in other areas in automotive vehicles (for example braking systems), and also in non automotive fields, those skilled in the art of vehicle seat design would not generally from a practical stance consider using hydraulic powered seat adjustment systems. Indeed the conventional trend is away from hydraulics in general in automotive applications and to electric powered systems. A distinction should also be drawn between hydraulic or fluid powered adjustment systems, and the more basic and simple hydraulic locking systems and/or damper arrangements.
A particular problem with seat adjustment arrangements, and in particular fluid powered arrangements, for automotive use is to provide adequate locking of the seat adjustment. For automotive use it is a requirement that the seat and seat portions once set are securely locked and fixed under all operating conditions and especially in the event of a vehicle crash. In a vehicle crash or impact large forces can be applied to the seat and seat portions which can generate extremely high pressures within a hydraulic adjustment system, which are significantly above the normal operating pressures and for example may be in the region of 1700 bar. The adjustment system must be capable of withstanding these pressures and maintain the locked position of the seat or seat portion. As a result the pipework, pump, actuators, and control valve need to be significantly oversized, and built to a much higher quality, than is required to simply withstand the normal operating conditions and pressure. This increases the resultant costs. In addition even under normal operating conditions leakage from or within the pipework, control valve and pump can undesirably result in movement of the set seat positions. To prevent this the seals within the pump, pipework and control valves must be built to a high quality and standard with resultant cost implications.
To address the problems associated with crash loading and the high pressures generated in fluid powered adjustment systems it has been proposed in co-pending UK patent application number 0324558.6, in the name of Lear Corporation, to incorporate system protection valves within the actuator. These system protection valves are adapted to be activated in the event of the pressure within the actuator exceeding a predetermined level and close off the inlet and outlet of the actuators. This isolates or limits the transmission of high pressures from the actuator to the remainder of the hydraulic system to protect the remainder of the hydraulic system from the excessive pressure which may be generated in the actuators in the event of crash loading. Whilst such system protection valves provide an improvement, and limit the pressures to which the remainder of the hydraulic system is subjected, thereby reducing costs, they do not address the potential problems of locking the actuators during normal use when leakage through the control valves or other associated parts may allow the actuator to undesirably move.
U.S. Pat. Nos. 5,743,591, 3,760,911, 3,860,098 and 6,161,633 all disclose various manually operated, unpowered, hydraulic adjustable seat locking arrangements incorporating various manually activated control valves. U.S. Pat. No. 5,743,591further includes a crash sensing system which is normally open and closes in a crash condition. None of these prior proposals however address the above described specifc problems. U.S. Pat. Nos. 6,015,130 and 3,777,617 described non automotive hydraulically adjustable chair arrangements which are very different from automotive adjustable seats and automotive seat requirements. U.S. Pat. No. 5,076,647 discloses a relief valve although this is for a brake system.